Webfs is a tiny web server that SMPlayer will run in order to serve local files to chromecast.

How to play a video on chromecast

Start to play a video in SMPlayer, then select the option Play -> Play on Chromecast. (You can stop playback in SMPlayer after that).

That will open a web page, which will get the URL of the video. This web page can communicate with your chromecast device. Connect/disconnect, start playback. There are also controls for play, pause, volume, seek...

Subtitles are not supported yet

Although SMPlayer will open the web page with your default web browser this will probably only work with google chrome and chromium.